1. Field of the Invention
The present invention relates to a fuel vapor control device which feeds vaporized fuel generated in a float chamber of a carburetor to a charcoal canister so that the vaporized fuel is absorbed in the charcoal canister during the time in which an engine is stopped.
2. Description of the Related Art
The fuel vapor control device feeds vaporized fuel generated in the float chamber of a carburetor to the charcoal canister to be absorbed therein when the engine is stopped, in order to prevent the intake system of the engine from being filled with the vaporized fuel. If the intake system is filled with the vaporized fuel, the air-fuel mixture becomes overrich when starting the engine, and thus it becomes difficult to start the engine. However, as almost all light gasolines have a low boiling point, i.e., vaporize at a low temperature, if the float chamber communicates with the charcoal canister for the whole period during which the engine is stopped, the amount of fuel vapor in the intake system is decreased to a point where it becomes difficult to start the engine after it has been stopped for a long time.
Japanese Unexamined Utility Model Publication No. 53-152020 shows a construction in which a passage connecting the float chamber and the charcoal canister is opened and closed according to the temperture of the cooling water of the engine, so that the vaporized fuel does not flow into the charcoal canister when the engine temperature is relatively low, i.e., a temperature at which light gasoline is vaporized. In this construction, a valve opens a passage connecting the float chamber and the charcoal canister when the temperature is higher than the predetermined value. That is, the valve opens from just after the engine is stopped and the temperature affecting the valve is above the predetermined value, until the temperature affecting the valve drops below that predetermined value.
In the above described conventional device, if the temperature at which the valve opens is set to a higher value to advance the time at which the valve is close, so as to improve the starting of the engine after it has been stopped for a long time, the time at which the valve opens just after the engine is stopped is delayed. Therefore, just after the engine is stopped, the intake system of the engine is filled with vaporized fuel generated in the float chamber of the carburetor, and thus the engine becomes difficult to start when hot. Conversely, if the temperature at which the valve opens is set to a lower value to enable the engine to be easily started just after the engine is stopped, the time at which the valve closes again after the engine has been stopped for a long time is delayed. As a result, the valve is open for a longer period and thus the amount of light gasoline vapor generated in the float chamber of the carburetor is decreased, making it more difficult to start the engine when cold. The above construction will be explained in more detail later, with reference to the drawings.